The industry of display apparatuses has studied for flat-type displays (display apparatuses) that can satisfy the demand for a thin thickness, a light weight, a large-sized screen, and fine definition. Liquid crystal displays, plasma displays, electro luminescence displays, field emission displays and the like are examples of such flat-type display. Among those, the field emission displays draw attention for their high definition and low power consumption.
An example of conventional filed emission displays is one disclosed in Japanese Publication of Unexamined Patent Application “Tokukai No. 2002-124199 (published on Apr. 26, 2002)”.
In the field emission display, as shown in FIG. 11, a cathode electrode film 202 is provided on a glass substrate 201 that functions as a base plate. On the cathode electrode film 202, a large number of emitters 203 are provided in matrix. The emitters 203 are made of a metal such as molybdenum (Mo) or the like. Typically, the emitters 203 have a circular cone-shape whose peak is sharp, and has a size not more than 1 μm. Moreover, a gate electrode film 205 is provided on that portion of the cathode electrode film 202 which surrounds the emitters 203, with an insulator layer 204 sandwiched therebetween.
Above the glass substrate 201, which functions as a base plate, and on which such emitters 203 and the like are provided, a glass substrate 206 is so provided as to face the glass substrate 201. The glass substrate 206 functions as a face plate. A surface of the glass substrate 206 which faces the glass substrate 201 is coated with a fluorescent material 207. On the fluorescent material 207, an anode electrode film 208 is provided.
The glass substrate 201 functioning as the base plate and the glass substrate 206 functioning as the face plate are spaced by a spacer (not shown). A space therebetween is a vacuum gap having a present distance therebetween.
A relatively negative voltage supplied from a scanning circuit 209 is applied on the cathode electrode film 202, whereas a relatively positive voltage supplied from a control circuit 210 is applied on the gate electrode film 205. Further, a positive voltage that is higher than the voltage applied on the gate electrode film 205 is applied on the anode electrode film 208. The voltage applied on the anode electrode film 208 is supplied from an accelerating power source 211. As a result, due to an electron tunnel effect, electrons are emitted into the vacuum gap from the sharp circular cone-shaped emitters 203 by an electric field produced when a voltage is applied between the cathode electrode film 202 and the anode electrode film 208. The fluorescent material 207, which is provided on that surface of the glass substrate 206 which faces the glass substrate 201 functioning as the base plate, is struck with the electrons emitted, in pattern, from the emitters 203. As a result, the fluorescent material 207 emits light.
Incidentally, it is very important for the field emission display that the emitters 203 for emitting the electrons are aligned orderly on the glass substrate 201, for operating the field emission display without damaging the emitters 203 and uneven screen luminescence, but with improved luminescence.
Explained below is how the field emission display is manufactured, especially how the emitters are formed, referring to FIGS. 12(A) to 12(E). Here, a spin deposition method is discussed, for example.
The field emission display is manufactured as follow. To begin with, a cathode electrode film 222, an insulating film 223, and a gate electrode film 224 are formed on a glass substrate 221 that functions as a base plate, as shown in FIG. 12(A). Next, as shown in FIG. 12(B), by using, as a mask, a resist pattern formed by the photolithography, etching is carried out so as to remove the electrode film 224 and the insulating film 223 selectively, thereby forming openings 225 orderly in matrix. After that, as shown in FIG. 12(C), a sacrificial film 226 is spin-deposited so as to coat a top surface and a side surface of the gate electrode film 224. The spin deposition of the sacrificial film 226 is carried out at a low angle with respect to the glass substrate 221.
Then, as shown in FIG. 12(D), metal such as molybdenum (Mo) or the like, is deposited. The deposition of the metal is carried out vertically to the glass substrate 221. As a result, emitters 228 made of the metal such as molybdenum (Mo) or the like are formed on the cathode electrode film 222, the emitters 228 having a circular cone shape with sharp peak and having a size of not more than 1 μm, for example.
Thereafter, as shown in FIG. 12(E), the sacrificial layer 226 is etched so as to remove a metal layer 227 that is made of molybdenum (Mo) or the like and is unnecessary. Note that the spin deposition may be carried out when the emitters 228 are formed.
In this way, the emitters 228 made of the metal such as molybdenum (Mo) or the like are formed orderly on the cathode electrode film 222, the emitters 228 having a circular cone shape with sharp peak and having a size of not more than 1 μm.
Incidentally, in order to manufacture the field emission display in the above fashion, it is necessary to form the openings 225 having a fine size and being aligned orderly, and then form the emitters 228 therein. Otherwise, the emitters 228 cannot be formed with a sharp circular cone shape and fine size, and aligned orderly on the glass substrate 221. Moreover, for the formation of the emitters 228, it is necessary that the sacrificial layer 226 be formed, by the spin deposition, on the gate electrode film 224 having the openings 225 and then the emitters 228 having the sharp circular cone shape be formed in the openings 225.
Besides the above-discussed method in which the resist pattern formed by the photolithography is used as the mask, the formation of the openings 225 having a fine size can be carried out by a method suggested by Japanese Publication of Unexamined Patent Application, Tokukai No. 2001-216888 (published on Aug. 10, 2002) titled “Manufacturing method and manufacturing apparatus of field emission display”. In the method suggested by this publication, a plurality of laser spots in a predetermined size are formed at once on a thin film on a substrate by using a laser and an micro lens array, so as to form openings in the thin film.
It is possible to form the openings that is orderly aligned, by using the methods of making fine openings.
Incidentally, in the conventional manufacturing methods of the field emission display, it is necessary that the emitters be formed in the openings by the spin deposition or the like method after the formation of the openings.
However, the use of the spin deposition for the formation of the emitter has such problems that, depending on conditions of the spin deposition and the like factors, the circular cone-shaped emitters thus formed may have uneven heights, uneven angles of its slope, uneven peak shapes, and the like. Such unevenness generally results in uneven field emission.
Especially, the use of the spin deposition cannot form the emitters that have a sharp peak, thereby resulting in low field emission efficiency and high power consumption.
Moreover, this largely affects reproducibility and productivity, thereby increasing cost of producing a large number of the emitters on a glass substrate.
Further, the spin deposition requires a system for accurate movement and rotation for depositing. This leads to a high cost.
Furthermore, it is necessary to form and then remove the sacrificial layer. This requires extra steps thereby increasing the cost.